Differential Diagnosis of Hypocalcemia

Hypocalcemia (low serum calcium) has a wide differential that includes disorders of parathyroid hormone (PTH) secretion or action, magnesium deficiency, and conditions causing malnutrition or malabsorption. The correct combination here is 1, 2 and 3 (Hypomagnesaemia, Chronic alcoholism, and Pseudohypoparathyroidism), while Paget's disease is not a cause of hypocalcemia.

Evaluating Each Statement

• 1. Hypomagnesaemia — Correct. Magnesium is required both for PTH release from the parathyroid glands and for peripheral PTH action on bone and kidney. Severe hypomagnesemia causes a functional hypoparathyroid state (impaired PTH secretion and end-organ resistance), producing hypocalcemia that will not correct with calcium replacement alone unless magnesium is also repleted.
• 2. Chronic alcoholism — Correct. Chronic alcohol use commonly causes poor dietary intake, magnesium and vitamin D deficiency, malabsorption, and pancreatitis-related fat malabsorption (with calcium soap formation). Alcoholism is thus a well-recognized, multifactorial cause of hypocalcemia, largely mediated through the hypomagnesemia and nutritional deficiency it produces.
• 3. Pseudohypoparathyroidism — Correct. This is a genetic disorder of PTH resistance (typically due to GNAS gene mutations impairing Gsα signaling at the PTH receptor). Despite normal or elevated PTH levels, target organs fail to respond, resulting in hypocalcemia with hyperphosphatemia, making it a classic differential diagnosis of hypocalcemia.
• 4. Paget's disease — Incorrect. Paget's disease is a disorder of excessive, disorganized bone remodeling (increased osteoclastic resorption followed by disorganized osteoblastic new bone formation). Serum calcium and phosphate levels are typically normal; hypercalcemia may rarely occur (e.g., with prolonged immobilization), but hypocalcemia is not a recognized feature. It therefore does not belong in the differential diagnosis of hypocalcemia.

Conclusion

Since hypomagnesemia, chronic alcoholism, and pseudohypoparathyroidism are all established causes of hypocalcemia, while Paget's disease is a disorder of bone turnover with normal (or occasionally high) calcium, the correct combination is 1, 2 and 3.